This invention relates to a thermoplastic elastomer composition.
Thermoplastic elastomers are known materials and recently their uses are being steadily increased including parts of automobiles, household appliances, etc. because of their low hardness and flexible properties and their moldability by the methods such as extrusion molding, injection molding, etc. like the conventional thermoplastic resins.
Especially, olefinic thermoplastic elastomers have low specific gravity, heat resistance and superior balance in properties in addition to the above properties and hence are in increased demand especially in the field of automobile parts also due to the trend of lightening of automobiles. Recently, they have been found to have their uses also in the field of injection molding of large articles such as bumpers of automobiles. There are movements to heighten fashionability by painting the surface of bumpers in the same colors as the bodies.
Furthermore, printing is often made on household appliances to increase decorative effects.
This invention relates to a thermoplastic elastomer composition capable of providing molded products improved in surface processabilities such as adhesiveness, paintability and printability together with impact resistance and heat resistance and contemplates use for parts of automobiles and household appliances as mentioned above.
Hitherto, compositions comprising olefinic copolymer rubbers or olefinic plastics have been well known as olefinic thermoplastic elastomers. However, owing to their non-polarity, in many cases, surface processing for improvement of adhesion, paintability, etc. are difficult.
In order to solve these problems, a medium called "primer", typical composition of which comprises halogenated polypropylene and toluene, is used as a layer between olefinic thermoplastic elastomer and adhesives and paint to further improve the compatibility therebetween.
However, due to expensiveness of the primer per se and addition of one extra step, the cost of final products increases and thus further improvement has been demanded.
For improvement of adhesion, modification of the surface of polypropylene molded products by physical or chemical etching has been studied and employed. However, the step of this method is more complex than the primer coating step and besides modification of the molded products may be caused depending on the etching conditions and improvement is insufficient.
For improvement of paintability, there has been employed a method of imparting polarity to the surface of molded products by irradiation with plasma in place of coating with primer. However, this method has not yet provided satisfactory results in that the plasma irradiation step is carried out in batch system and treatment becomes ununiform for molded products of some shapes.